There is conventionally provided an image reading apparatus that causes two image reading units to read images on the obverse and reverse surfaces of an original and is mounted with both white and black background members. To suppress show-through when an original is a thin paper sheet, the black surface is arranged behind the original. To suppress reading of a portion around an original in black when the original is of an irregular size, the white surface is arranged behind the original.
To switch the background color, a movable mechanism is required. In an image reading apparatus described in PTL 1, there is proposed a method of switching the background color by causing the movable mechanism to move one of reading units for the obverse and reverse surfaces in a conveyance direction to change the position of an image reading portion. In this arrangement, when the reading unit moves, a white background plate or a black background plate is arranged to face the reading positions of the image reading units for both the obverse and reverse surfaces.